Semiconductor device arrangement with a first semiconductor device and with a plurality of second semiconductor devices

ABSTRACT

Disclosed is a semiconductor device arrangement including a first semiconductor device having a load path, and a plurality of second transistors, each having a load path between a first and a second load terminal and a control terminal. The second transistors have their load paths connected in series and connected in series to the load path of the first transistor, each of the second transistors has its control terminal connected to the load terminal of one of the other second transistors, and one of the second transistors has its control terminal connected to one of the load terminals of the first semiconductor device.

This application is a continuation of U.S. Non-Provisional applicationSer. No. 14/633,411, filed on Feb. 27, 2015, entitled “SemiconductorDevice Arrangement with a First Semiconductor Device and with aPlurality of Second Semiconductor Devices, which is a continuation ofU.S. Non-Provisional application Ser. No. 13/978,373, filed on Nov. 20,2013, entitled “Semiconductor Device Arrangement with a FirstSemiconductor Device and with a Plurality of Second SemiconductorDevices,” now U.S. Pat. No. 8,970,262, which is a National Stage Entryof PCT Application PCT/EP2012/050245 filed on Jan. 9, 2012 that claimspriority to the following applications: U.S. patent application Ser. No.12/986,784 filed on Jan. 7, 2011 entitled “Transistor Arrangement with aFirst Transistor and With a Plurality of Second Transistors,” now U.S.Pat. No. 8,455,948; and U.S. patent application Ser. No. 13/275,151filed on Oct. 17, 2011 entitled “Semiconductor Device Arrangement with aFirst Semiconductor Device and with a Plurality of Second SemiconductorDevices,” now U.S. Pat. No. 8,569,842 that is a continuation-in-part ofU.S. Non-Provisional application Ser. No. 12/986,784 mentioned above,all of which applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

Embodiments of the present invention relate to a semiconductor devicearrangement with a first semiconductor device, such as a transistor or adiode, and with a plurality of second semiconductor devices, suchtransistors, in particular low-voltage transistors.

BACKGROUND

One important aim in the development of power semiconductor devices,such as power transistors or power diodes, is to produce devices with ahigh voltage blocking capability but, nevertheless, a low on-resistance(RoN) and which have low switching losses.

Power transistors usually include a drift region arranged between a bodyregion and a drain region and doped lower than the drain region. Theon-resistance of a conventional power transistor is dependent on thelength of the drift region in a current flow direction and on the dopingconcentration of the drift region, wherein the on-resistance decreaseswhen the length of the drift region is reduced or when the dopingconcentration in the drift region is increased. However, reducing thelength of the region or increasing the doping concentration reduces thevoltage blocking capability.

One possible way to reduce the on-resistance of a power transistor for agiven voltage blocking capability is to provide compensation regions inthe drift region, wherein the compensation regions are dopedcomplementary to the drift region. Another possible way is to providefield plates in the drift region which are dielectrically insulated fromthe drift region and which are, for example, connected to a gate orsource terminal of the transistor. In these types of power transistors,the compensation zones or the field plates partly “compensate” dopingcharges in the drift region when the component is in its off-state. Thisallows to provide a higher doping of the drift region—which reduces theon-resistance—without reducing the voltage blocking capability.

A power diode (pin diode) usually includes a low doped drift or baseregion between a first emitter region of a first doping type and asecond emitter region of a second doping type. A power diode isconfigured to block when a voltage with a first polarity (blockingvoltage) is applied between the first and second emitter regions, and isconfigured to conduct a current when a voltage with a second polarity isapplied between the first and second emitter regions. In the conductingstate, however, a charge carrier plasma with charge carriers of thefirst and second type (p-type and n-type charge carriers) is generatedin the base region. The amount of charge carrier plasma stored in thebase region is dependent on a length of the base region and is,therefore, dependent on the voltage blocking capability, where theamount of charge carrier plasma increases when the voltage blockingcapability increases. This charge carrier plasma has to be removedbefore the diode may block upon applying a blocking voltage.

These known devices, however, have a high output capacitance. There is,therefore a need to provide a power semiconductor device with a highvoltage blocking capability, a low on-resistance and a low outputcapacitance.

SUMMARY

A first embodiment relates to a semiconductor device arrangementincluding a first semiconductor device having a load path, and aplurality of second transistors, each having a load path between a firstand a second load terminal and a control terminal. The secondtransistors have their load paths connected in series and connected inseries to the load path of the first transistor. Each of the secondtransistors has its control terminal connected to the load terminal ofone of the other second transistors, and one of the second transistorshas its control terminal connected to one of the load terminals of thefirst semiconductor device.

A second embodiment relates to a transistor arrangement. The transistorarrangement includes a first transistor with a drift region, a pluralityof second transistors each having a source region, a drain region and agate electrode. The second transistors are connected in series to form aseries circuit which is connected in parallel with the drift region ofthe first transistor. The source regions of the second transistors arecoupled to the drift region and the gate electrodes of the secondtransistors are coupled to the drift region such that the source regionand the gate region of each of the second transistors are coupled to thedrift region at different positions.

A third embodiment relates to a circuit arrangement including atransistor arrangement with a first transistor having a load path and acontrol terminal and with a plurality of second transistors, each havinga load path between a first and a second load terminal and a controlterminal. The second transistors have their load paths connected inseries and connected in series to the load path of the first transistor,and each of the second transistors has its control terminal connected tothe load terminal of one of the other second transistors, and one of thesecond transistors has its control terminal connected to one of the loadterminals of the first transistor. The circuit arrangement furtherincludes a capacitive storage element connected to the load terminal ofone of the second transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples will now be explained with reference to the drawings. Thedrawings serve to illustrate the basic principle, so that only aspectsnecessary for understanding the basic principle are illustrated. Thedrawings are not to scale. In the drawings the same reference charactersdenote like features.

FIG. 1 illustrates a transistor arrangement with a first transistorhaving a drift region, and with a plurality of second transistorsconnected in series with each other and having source regions and gateelectrodes coupled to the drift region of the first transistor.

FIGS. 2A and 2B show the equivalent circuit diagrams of the transistorarrangement of FIG. 1 when the first transistor is switched on (FIG. 2A)and when the first transistor is switched off (FIG. 2B).

FIG. 3 schematically illustrates a first embodiment for implementing thefirst and second transistors in a semiconductor body.

FIG. 4 schematically illustrates a first embodiment of a substratesection of the arrangement of FIG. 3.

FIG. 5 schematically illustrates a second embodiment of a substratesection of the arrangement of FIG. 3.

FIGS. 6A and 6B illustrates a further embodiment for implementing sourceand body regions and a gate electrode of the first transistor.

FIGS. 7A to 7C illustrates a second embodiment for implementing thesecond transistors.

FIGS. 8A to 8C schematically illustrates a further embodiment forimplementing the second transistors.

FIG. 9 schematically illustrates a transistor arrangement which includessecond transistors according to FIG. 8.

FIG. 10 illustrates a top view on a transistor arrangement in which thesecond transistors include several transistor cells connected inparallel.

FIG. 11 illustrates a top view on a transistor arrangement according toa further embodiment in which the second transistors includes severaltransistor cells connected in parallel.

FIG. 12 illustrates a further embodiment of a transistor arrangementwith a first transistor having a drift zone.

FIG. 13 illustrates another embodiment of a transistor arrangement witha first transistor and a plurality of second transistors.

FIGS. 14A and 14B show the equivalent circuit diagrams of the transistorarrangement of FIG. 13 when the first transistor is switched on (FIG.14A) and when the first transistor is switched off (FIG. 14B).

FIG. 15 illustrates an embodiment of the arrangement of FIG. 13 in whichthe second transistors are implemented as JFETs.

FIG. 16 illustrates an embodiment of the arrangement of FIG. 13 in whichthe second transistors are implemented as nanotube devices or HEMTS.

FIG. 17 illustrates a first embodiment of an integrated circuit thatincludes a circuit arrangement according to FIG. 13.

FIG. 18 illustrates a second embodiment of an integrated circuit thatincludes a circuit arrangement according to FIG. 13.

FIG. 19 illustrates a third embodiment of an integrated circuit thatincludes a circuit arrangement according to FIG. 13.

FIG. 20 illustrates a top view of a semiconductor body according inwhich a first semiconductor device and a plurality of secondsemiconductor devices each including several FINFET cells areimplemented.

FIG. 21 illustrates a vertical cross sectional view of one secondsemiconductor device including several FINFET cells connected inparallel.

FIGS. 22A to 22C illustrates a further embodiment of one secondsemiconductor device including several FINFET cells connected inparallel.

FIG. 23 illustrates two second semiconductor devices of the typeillustrated in FIG. 21 connected in series.

FIGS. 24A and 24B illustrates an embodiment of a second transistor thatincludes means that prevent the accumulation of minority chargecarriers.

FIG. 25 illustrates a first embodiment of a circuit arrangement with afirst transistor and second transistors that includes means for clampinga voltage across the second transistors.

FIG. 26 illustrates a second embodiment of a circuit arrangement with afirst transistor and second transistors that includes means for clampinga voltage across the second transistors.

FIGS. 27A and 27B illustrates a first embodiment of a second transistorthat includes integrated voltage clamping means.

FIG. 28 illustrates a second embodiment of a second transistor thatincludes integrated voltage clamping means.

FIG. 29 illustrates an embodiment of a circuit arrangement with a diodeand with second transistors connected in series with the diode.

FIG. 30 illustrates the application of a circuit arrangement with afirst transistor and with a plurality of second transistors in a voltageconverter.

FIG. 31 illustrates a first embodiment of the circuit arrangement and apower supply circuit of the voltage converter in detail.

FIG. 32 illustrates a second embodiment of the circuit arrangement and apower supply circuit of the voltage converter in detail.

FIG. 33 illustrates a first embodiment of the circuit arrangement and apower supply circuit of the voltage converter in detail.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 schematically illustrates a first embodiment of a transistorarrangement. The transistor arrangement includes a first transistor 1implemented as an MOS transistor. The first transistor 1 includes asource terminal S which electrically contacts a source region, a gateterminal G which electrically contacts a gate electrode, and a drainterminal D which electrically contacts a drain region. In FIG. 1, thefirst transistor 1 is represented by its circuit symbol, so that thesource S, gate G, and drain D terminals but not the source region, thegate electrode and the drain region are shown.

The first transistor 1 of FIG. 1 is a power transistor which furtherincludes a drift region. The drift region is arranged between the drainterminal D and the source terminal S, and is a doped semiconductorregion which mainly defines the voltage blocking capability of the firsttransistor 1. A conventional circuit symbol of an MOS transistor doesnot explicitly show or illustrate the drift region of the MOStransistor. However, since the drift region has a relevant function inthe transistor arrangement illustrated in FIG. 1, the drift region ofthe first transistor 1, additionally to the circuit symbol, is alsoillustrated in FIG. 1. The drift region is represented by a seriescircuit with resistors 2 ₀, 2 ₁, 2 ₂, 2 _(n) connected between the drainterminal D and a body region (not shown in FIG. 1) of the firsttransistor 1. Since the drift region is a doped semiconductor region,each of the resistors 2 ₀-2 _(n) illustrated in FIG. 1 represents theresistance of one section of the drift region.

Before explaining the other features of the transistor arrangement ofFIG. 1, the basic operating principle of the first transistor 1 with thedrift zone will be explained. For explanation purposes it will beassumed that the first transistor 1 is an n-type enhancement MOSFET (asrepresented by the circuit symbol in FIG. 1). However, any other type ofMOS transistor, like an n-type depletion transistor, a p-typeenhancement transistor, a p-type depletion transistor, or an IGBT, canbe used as well. The different types of transistors have the sameoperating principle, which is that they can be switched on and off byapplying a suitable drive potential to the gate terminal G or a suitabledrive voltage between the gate terminal G and the source terminal S,respectively. The difference is that the control voltages (gate-sourcevoltages) at which the individual transistors are switched on and offare different for the different types of transistors.

The n-type enhancement MOSFET 1 of FIG. 1 can be switched on by applyinga positive voltage between the gate and the source terminals G, S. Inthe on-state of the first transistor 1 a resistance between the drainterminal D and the source terminal S, which is also referred to ason-resistance, is mainly defined by the drift region, in particular, bythe doping concentration of the drift region and the length of the driftregion in the current flow direction. A drain-source voltage V_(DS) ofthe first transistor 1 mainly drops across the drift region when thetransistor is in its on-state. This voltage drop is dependent on theon-resistance of the first transistor 1 and on a load current flowingthrough the transistor. The first transistor 1 can, for example, be usedfor switching a load current through a load Z. For this, the firsttransistor 1 can be connected in series with a load Z between terminalsfor a positive supply potential V+ and a negative supply potential orreference potential GND. When the first transistor 1 is switched on, thesupply voltage which is present between the supply terminals mainlydrops across the load Z, wherein the voltage drop across the firsttransistor 1 is defined by the load current and the on-resistance of thefirst transistor 1. In conventional power transistors this voltage dropis, for example, typically in the range of between 0.1V and 3V.

When the first transistor 1 is switched off, the voltage drop across thefirst transistor 1 increases. In the off-state of the first transistor1, the voltage V_(DS) which is applied between the drain and sourceterminals D, S mainly drops across the drift region which, besides theon-resistance, also defines the voltage blocking capability of the firsttransistor 1. This is because in the off-state, the drift zone isdepleted of charge carriers. The voltage blocking capability and,therefore, the voltage drop V_(DS) across the drift region can be in therange of between several 10 volts (V) to several 100 volts (V) up to 1kV and more. This voltage blocking capability is dependent on thespecific implementation of the drift and is in particular dependent on adoping concentration of the drift region and of a length of the driftregion in a current flow direction.

In order to reduce the electrical resistance between the drain and thesource terminals D, S when the first transistor 1 is switched on, thetransistor arrangement of FIG. 1 further includes a plurality of secondtransistors 3 ₁, 3 ₂, 3 _(n). These second transistors are alsoimplemented as MOS transistors which each include a gate terminalcontacting a gate electrode, a drain terminal connecting a drain regionand a source terminal connecting a source region. These secondtransistors 3 ₁, 3 ₂, 3 _(n) are connected in series, with the seriescircuit with the second transistors 3 ₁, 3 ₂, 3 _(n) being connected inparallel with the drift region. Further, the source terminal or sourceregion of each of the second transistors is coupled to the drift region.Optionally, the gate terminal or gate electrode of each of the secondtransistors 3 ₀, 3 ₁, 3 ₂, 3 _(n) is also coupled to the drift region.In the following, when reference is made to an arbitrary one of thesecond semiconductor devices (transistors) or to the plurality of thesecond semiconductor devices, and when no differentiation betweenindividual second semiconductor devices is required, reference number 3_(i) will be used to denote the second semiconductor devices and theirindividual parts.

In the embodiment illustrated in FIG. 1, each of the second transistors3 ₁, 3 ₂, 3 _(n) is connected in parallel with one section of the driftregion, wherein the individual sections of the drift region arerepresented by the resistors 2 ₁, 2 ₂, 2 _(n) in FIG. 1. The secondtransistors 3 ₁, 3 ₂, 3 _(n) are switched on and off dependent on thevoltage drop across the drift region, so that no additional externalterminals are required for controlling the second transistors, whereinthe second transistors may influence or define the voltage across thedrift region. The overall transistor arrangement illustrated in FIG. 1can be switched on and off like a conventional transistor by applying asuitable control voltage between the gate and source terminals G, S ofthe first transistor 1.

In FIG. 1, the gate electrodes and the source regions of the secondtransistors 3 ₁, 3 ₂, 3 _(n) are coupled to the drift region such thateach of the second transistors 3 ₁, 3 ₂, 3 _(n) is controlled by thevoltage drop across one associated section of the drift region. In FIG.1, a first one 3 ₁ of the second transistors is, for example, controlledby a voltage drop V2 ₀ across a first section 2 ₀ of the drift region, asecond one 3 ₂ of the transistors is controlled by a voltage drop V2 ₁across a second section 2 ₁ of the drift region, etc. For this, thefirst drift region section 2 ₀ is connected between gate and source ofthe second transistor 3 ₁, the second drift region section 2 ₁ isconnected between gate and source of the transistor 3 ₂, etc. Thecontrol voltage of any of the second transistors is dependent on thevoltage drop V_(DS) across the drift region and is dependent on thedistance between the positions at which the gate electrode and thesource region of the second transistor is coupled to the drift region.

In order to reduce the on-resistance of the first transistor 1 with thedrift zone, the second transistors 3 ₁, 3 ₂, 3 _(n) are switched on whenthe first transistor 1 is in its on-state, as the voltage drop isbecoming small across the drift zone. When the first transistor 1 is inits off-state, the second transistors 3 ₁, 3 ₂, 3 _(n) are switched off,because of the high voltage drop V_(DS) over the drift zone with thedepleted drift zone charge carrier. When the first transistor 1 is inits on-state, the resistance of its drift region is low, so that avoltage drop V_(DS) across the drift region is low and, consequently,the voltage drops V2 ₀, . . . , V2 _(n) across the individual driftregion sections 2 ₀, . . . , 2 _(n) are low. When the first transistor 1is in its off-state, the voltage drop V_(DS) across the drift region issignificantly higher than in the on-state and, consequently, the voltagedrops V2 ₀, . . . , V2 _(n) across the individual drift region sectionsare also significantly higher than in the on-state.

According to one embodiment, the positions at which the source regionsand the gate electrodes of the individual transistors are connected tothe drift region are selected such that the absolute value of the drivevoltage between the gate electrode and the source region is very small,e.g. between 0.005V and 0.5V when the first transistor 1 is in itson-state, and is e.g. between 1V and 30V when the first transistor 1 isin its off-state.

The drive voltage of the second transistors 3 ₁-3 _(n) is low, like inthe absolute range of between 0.005V and 0.5V, when the first transistor1 is on, and the voltage drop over the second transistors 3 ₁-3 _(n) ishigh, like in the absolute range of between 1V and 30V, when the firsttransistor 1 is off. The individual second transistors 3 ₁-3 _(n) areselected such that they can be switched on by the low voltage dropacross their associated drift region section when the first transistoris in its on-state, and that they can be switched off by the highvoltage drop across their associated drift region section if the firsttransistor 1 is in its off-state. In FIG. 1, the second transistor areconnected such that positive voltage drops across the individual driftregion sections result in negative drive voltages of the individualsecond transistors. For example, V_(GS1)=−V2 ₀, where V_(GS1) is thecontrol voltage (gate-source voltage) of first transistor 3 ₁.Equivalently, V_(GS2)=−V2 ₁, where V_(GS2) is the control voltage of thesecond transistor 3 ₂. When the first transistor 1 is an n-typetransistor, the second transistors are selected such that they can beswitched on by a low negative control voltage and that they can beswitched off by a higher negative control voltage. Suitable transistorsare, for example, n-type depletion transistors. However, p-typedepletion transistors can be used as well. In this case, the secondtransistors are coupled to the drift region such that a low positivecontrol voltage is applied to the second transistors when the firsttransistor 1 is in its on-state and that a higher positive controlvoltage is applied to the second transistors when the first transistor 1is in its off-state. Even enhancement transistors could be used for thesecond transistors when the work function of the gate electrode ischosen such that an n-type transistor is already switched on at a lownegative drive voltage and that a p-type transistor is switched on at alow positive drive voltage.

In the embodiment illustrated in FIG. 1, a first section 2 ₀ of thedrift region, which is the section arranged most distant to the drainterminal D and closest to the source terminal S, serves to generate thecontrol voltage for the first one 3 ₁ of the second transistors, but hasno second transistor connected in parallel. Optionally, a secondtransistor 3 ₀ is also connected in parallel with this first driftregion section 2 ₀, wherein the gate terminal of this transistor 3 ₀ isconnected to the source terminal of the first transistor 1.

FIGS. 2A and 2B show the equivalent circuit diagram of the transistorarrangement of FIG. 1 when the first transistor 1 is in its on-state(see FIG. 2A) and when the first transistor 1 is in its off-state (seeFIG. 2B). Referring to FIG. 2A, when the first transistor 1 is in itson-state the second transistors 3 ₁-3 _(n) and the optional secondtransistor 3 ₀ are switched on and, therefore, provide a current pathparallel to the drift region which helps to reduce the overallon-resistance of the transistor arrangement. This current path parallelto the drift region is represented in FIG. 2A by a series circuit withresistors R3 ₁, R3 ₂, R3 _(n) (and optional R3 ₀) wherein each of theseresistors represents the on-resistance of one of the second transistors3 ₁-3 _(n). The second transistors 3 ₀, 3 ₁-3 _(n) are low voltagetransistors which according to one embodiment have an on-resistancewhich is lower than the resistance of the drift region sections 2 ₀, 2₁-2 _(n).

When the first transistor 1 is switched off and, therefore, the secondtransistors are also switched off—as the voltage V_(DS) drops over thedrift zone—the series circuit with the gate-source capacitances of thesecond transistors 3 ₀, 3 ₁-3 _(n) dominate the function of the secondtransistors 3 ₀, 3 ₁-3 _(n). The drift zone is depleted of chargecarriers and therefore can be left away. In the off-state of the firsttransistor 1, the gate source capacitance of any one of the secondtransistors, like, e.g., transistor 3 ₂, stores those electrical chargeswhich, in the on-state of the first transistor 1, were required in theneighbouring transistor, like, e.g., transistor 3 ₁, for generating aconducting channel in the body region of this neighbouring transistor.Thus, electrical charges which are required for switching on and off theindividual second transistors are only shifted between the body regionof one second transistor and the gate-source capacitance of aneighbouring second transistor when the first transistor 1 transitionsfrom the on-state to the off-state, and vice versa. Thus, these chargesdo not have to be provided from externally via the drain and sourceterminals of the first transistor 1, resulting in a low outputcapacitance of the transistor arrangement.

In FIG. 2B, the gate-source capacitances C3 ₁-C3 _(n) (and C3 ₀ of theoptional transistor 3 ₀) are shown. These gate-source capacitancesdominate the behaviour of the arrangement when the second transistorsare in their off-state.

It should be noted that although in FIG. 1 only n=3 or n+1=4,respectively, second transistors 3 ₀, 3 ₁, 3 ₂, 3 _(n) are illustrated,the basic principle is not restricted to this number of secondtransistors. An arbitrary number of second transistors 3 ₀-3 _(n) can beconnected in series with each other and in parallel with the driftregion, wherein the number of second transistors 3 ₀-3 _(n) is dependenton the desired voltage blocking capability of the transistor arrangementwith the first transistor 1 and the second transistors 3 ₀-3 _(n). Sincethe second transistors 3 ₀-3 _(n) are low-voltage transistors theirvoltage blocking capability is significantly lower than the voltageblocking capability of the first transistor 1 with the drift zone. If,for example, the voltage blocking capability of the first transistorwith the drift zone is V_(DSmax) and the voltage blocking capability ofeach of the second transistors is V3 _(DSmax), then the number of secondtransistors at least to be connected in series with each other andparallel to the drift region is given by the quotient V_(DSmax)/V3_(DSmax).

FIG. 3 illustrates a first embodiment for implementing the transistorarrangement. In this embodiment, the transistor arrangement includes asemiconductor body 100 in which active semiconductor regions of thefirst transistor 1 and the second transistors 3 ₀-3 _(n) areimplemented. Active semiconductor regions of these transistors aresource regions, drain regions, body regions and, in case of the firsttransistor, the drift region. The semiconductor body may include aconventional semiconductor material such as, for example, silicon (Si).

Referring to FIG. 3, the first transistor 1 includes a source region 11electrically connected to the source terminal S and a drain region 15electrically connected to the drain terminal D. This transistor isimplemented as a lateral transistor, which means that the source regionn and the drain region 15 are arranged distant to one another in alateral or horizontal direction of the semiconductor body 100. The firsttransistor 1 further includes a drift region 2 adjoining the drainregion 15, and a body region 12 which is arranged between the sourceregion ii and the drift region 2. A gate electrode 13 serves to controla conducting channel between the source region 11 and the drift region 2and is arranged adjacent to the body region 12 and dielectricallyinsulated from the body region 12 by a gate dielectric 14. The firsttransistor 1 is in its on-state when an electrical potential is appliedto the gate electrode G which is suitable for inducing a conductivechannel between the source region 11 and the drift region 2 in the bodyregion 12.

The first transistor 1 is, for example, implemented as an n-type MOSFET.In this case, the source region 11, the drain region 15 and the driftregion 2 are n-doped. Further, the first transistor can be implementedas an enhancement transistor or as a depletion transistor. In an n-typeenhancement transistor the body region 12 is p-doped, i.e. is dopedcomplementarily to the source region 11 and the drift region 2. In adepletion transistor the body region 12 at least adjacent to the gatedielectric 14 includes an n-type channel region which extends from thesource region 11 to the drift region 2 and which can be depleted ofcharge carriers by applying a suitable control potential at the gateterminal G. The first transistor 1 could also be implemented as a p-typeenhancement or depletion transistor. In p-type transistors, theindividual semiconductor regions are doped complementarily to thecorresponding semiconductor regions in an n-type transistor.

Referring to FIG. 3, the active semiconductor regions of the secondtransistors are implemented in the drift region 2 or are implementedbetween the drift region 2 and a surface 101 of the semiconductor body100. At this surface 101 the source 11 and drain 15 regions areconnected to the source S and drain D terminals. In FIG. 3, only threesecond transistors 3 ₁, 3 ₂, 3 _(n) are shown. However, this is only anexample, the number n of second transistors is, of course, not limitedto n=3.

The individual second transistors are implemented in identical manner,so that in FIG. 3 reference characters are only indicated for a firstone 3 ₁ of these second transistors. These second transistors 3 ₁-3 _(n)each include a source region 41 and a drain region 42 arranged distantto the source region 41 in a lateral direction of the semiconductor body100. A body region 43 is arranged between the source region 41 and thedrain region 42. A gate electrode 44 is arranged adjacent to the bodyregion 43 and dielectrically insulated from the body region 43 by a gatedielectric 45 serves to control a conducting channel between the sourceregion 41 and the drain region 42. The source region 41 is electricallyconnected to a source electrode 51 which, in the embodiment of FIG. 3,also electrically contacts the body region 43. The drain region 42 iselectrically connected to a drain electrode 52.

In the transistor arrangement of FIG. 3, the second transistors 3 ₁-3_(n) are arranged next to each other in the current flow direction ofthe first transistor 1. The “current flow direction” is the direction inwhich the source region 11 and the drain region 15 of the firsttransistor are arranged distant to each other.

The source electrode of one second transistor is connected with thedrain electrode of one neighbouring second transistor, so that thesecond transistors 3 ₁, 3 ₂, 3 _(n) are connected in series with each.Further, the source terminals of the individual second transistors 3 ₁,3 ₂, 3 _(n) are coupled to the drift region 2. For explanation purposesit is assumed that the first transistor is an n-type transistor and thatthe second transistors 3 ₁, 3 ₂, 3 _(n) are also n-type transistors. Inthis case, the drain region 42 or the drain electrode 52 of each of thesecond transistors 3 ₁-3 _(n) is arranged closer to the drain region 15than the corresponding source region 41 of the transistor. Further, thedrain region 42 or the drain electrode 52 is connected to the sourceregion 41 or the drain electrode 52 of a neighbouring transistor which,in the embodiment of FIG. 3, is the neighbouring transistor in thedirection of the drain electrode 15. For example, the drain region 42 ofthe second transistor 3 ₁ is electrically connected to the source regionof the neighbouring transistor 3 ₂, wherein the transistor 3 ₂ is theneighbouring transistor to transistor 3 ₁ in the direction of the drainregion 15.

In FIG. 3, the second transistors 3 ₁-3 _(n) are planar transistorswhich have their gate electrode 44 arranged above the surface 101 of thesemiconductor body 100. In these transistors the body region 43 is dopedcomplementarily to the source region 41 and the drain region 42 and mayinclude a doped channel region (illustrated in dotted lines) of the samedoping type as the source region 41 and the drain region 42 and arrangedbetween the source region 41 and the drain region 42 and adjacent to thegate dielectric 44. Through these source electrodes the individualsecond transistors, which are connected in series, are also connected inparallel with the drift region 2. For example, the second transistor 3 ₁is connected in parallel with a first section (represented by resistor21 in FIG. 3) of the drift region 2 via its source electrode 51 and thesource electrode of the neighbouring second transistor 3 ₂. The secondtransistor 3 _(n) which of the plurality of second transistors 3 ₁, 3_(n) is arranged closest to the drain region 15 has its drain electrodeconnected to the drain region 15 at the end of the drift zone of thefirst transistor with the drift zone 2.

Further, the second transistors 3 ₁, 3 ₂, 3 _(n) have their gateelectrodes coupled to the drift region 2. Referring to FIG. 3, exceptfor the second transistor 3 ₁ which is arranged closest to the bodyregion 12 of the first transistor, the second transistors 3 ₂, 3 _(n)have their gate electrodes coupled to the source electrode of theneighbouring second transistor. In this case, the neighbouringtransistor of one of the second transistors is the transistor which isarranged next to the one transistor in the direction of the body region.If, for example, 3 _(i) denotes one of the second transistors and 3_(i)-i denotes a transistor which is arranged next to transistor 3 _(i)in the direction of the body region 12, then transistor 3 _(i) has itsgate terminal connected to the source terminal of transistor 3 _(i−1).However, this is only an example. One second transistor 3 _(i) couldalso have its gate terminal connected to the source terminal oftransistor 3 _(i−2), or 3 _(i−)which is the second or third transistoras seen from the position of the transistor 3 _(i) in the direction ofthe body region 12.

The second transistors 3 ₁-3 _(n) are controlled by the voltage dropacross the drift region 2 between those positions at which the sourceregion and the gate electrode of the second transistors 3 ₁-3 _(n) arecoupled to the drift region 2. This voltage drop is usually low when thefirst transistor 1 is in its on-state and is usually high when the firsttransistor is in its off-state. The positions at which the gateelectrodes 44 and the source regions 41 of the individual secondtransistors 3 ₁-3 _(n) are coupled to the drift region 2 are selectedsuch that when the first transistor is in the on-state the voltage dropbetween the source region 41 and the gate electrode 44 of each of thesecond transistors 3 ₁-3 _(n) is suitable to switch the secondtransistors 3 ₁-3 _(n) on, while when the first transistor 1 is in itsoff-state the (higher) voltage drop is suitable to switch the secondtransistors 3 ₁-3 _(n) off. In the embodiment illustrated in FIG. 3, thefirst transistor can be an n-type transistor 1 and the secondtransistors 3 ₁-3 _(n) can also be n-type transistors. In this case, thevoltage drops between the gate electrode 44 and the source regions 41 ofthe second transistors 3 ₁-3 _(n) are negative voltages which are lowwhen the first transistor is on and which are high, when the firsttransistor is off. The second transistors are selected such that theirthreshold voltage is low enough that these transistors 3 ₁-3 _(n) areswitched on at low negative drive voltages.

In an n-type first transistor, the second transistors 3 ₁-3 _(n) couldalso be implemented as p-type transistors. In this case, the gateelectrodes of the individual second transistors will have to beconnected to source terminals of the second transistors which arearranged in the direction of the drain region 15. These p-typetransistors are implemented such that they are switched on at a lowpositive voltage and that are switched off at a higher positive voltage.

In FIG. 3, only a semiconductor layer is illustrated in which the activesemiconductor regions of the first and second transistors 1, 3 ₁-3 _(n)are illustrated. This semiconductor layer can be arranged on anysuitable substrate. Referring to FIG. 4, which only shows a lowersection of the semiconductor layer with the active regions, the layerwith the active regions of FIG. 3 can be arranged on a semiconductorsubstrate no which is doped complementarily to the drift region 2. Thesubstrate could also extend to region 2, i.e. there is no drift zonedoping.

Referring to FIG. 5, the semiconductor layer with the active regions canalso be arranged on an SOI substrate. This SOI substrate includes asemiconductor substrate no and an insulation layer 120 arranged betweenthe substrate 110 and the semiconductor layer with the active regions.

In FIG. 3, the first transistor has a planar gate electrode 13, which isa gate electrode which is arranged above the surface 101 of thesemiconductor body 100. However, this is only an example. The firsttransistor 1 could be implemented with any other known gate topology aswell. FIGS. 6A and 6B illustrate further embodiments of a gate topologyof the first transistor. FIG. 6A shows a vertical cross section of thesemiconductor body 100 in that region, in which the source region 11,the body region 12 and the gate electrode are arranged, and FIG. 6Billustrates a horizontal cross section in a section plane A-A shown inFIG. 6A. The drain region or a drain terminal is not shown in FIGS. 6Aand 6B.

Referring to FIGS. 6A and 6B the gate electrode 13 is arranged intrenches which from the first surface 101 extend in a vertical directionof the semiconductor body 100. These trenches in a horizontal directionextend from the source region 11 to the drift region 2, wherein the bodyregion 12 is arranged between these trenches and separates the sourceregion 11 from the drift region 2. In a conventional manner, the gateelectrode 13 is dielectrically insulated from the body region 12 (andthe source and drift regions 11, 2) by the gate dielectric 14.

It should be noted that the second transistors 3 ₁-3 _(n) can also beimplemented with other geometries or topologies than illustrated in FIG.3. Further illustrative embodiments for implementing these secondtransistors are illustrated in FIGS. 7A to 7C and 8A to 8B.

FIG. 7A shows a perspective view of a second transistor 3 _(i) (3 _(i)represents any one of the second transistors explained before)implemented as a FINFET. FIG. 7B shows a vertical cross sectional viewand FIG. 7C shows a horizontal cross sectional view of this secondtransistor. FIGS. 7A, 7B, 7C only show a section of the semiconductorbody in which one second transistor is implemented. Active regions ofthe first transistor (besides a section of the drift region 2) andactive regions of neighbouring second transistors are not shown.

Referring to FIG. 7A, the source, drain and body regions 41, 42, 43 ofthis transistor are arranged in a fin-like semiconductor section 130(which will also be referred to as “semiconductor fin” in the following)above the drift region 2. In one horizontal direction, the source anddrain regions 41, 42 extend from sidewall 131 to sidewall 132 of thisfin-like semiconductor region 130. In a second direction which isperpendicular to the first direction the source and drain regions 41, 42are arranged distant from each other and are separated by the bodyregion 43. The gate electrode 44 (illustrated in dashed lines in FIG.7A) is dielectrically insulated from the fin-like semiconductor region130 by the gate dielectric 45 and is arranged adjacent to the bodyregion 44 one of the sidewalls 131, 132 and a top surface 133 of thisfin-like semiconductor region. In the embodiment illustrated in FIGS. 7Ato 7C, the gate electrode 44 and the gate dielectric 45 are formed oneach of the top surface 133 and each of the sidewalls 131, 132 of thesemiconductor fin 130. However, this is only example, according tofurther embodiments (not shown), the gate electrode 44 and the gatedielectric 45 are only formed on the top surface 133 or only on at leastone of the sidewalls 131, 132 of the semiconductor fin 130.

FIGS. 8A to 8B illustrate a further embodiment of one second transistor3 _(i) implemented as a FINFET having a semiconductor fin 130. Thetransistor 3 _(i) according to FIGS. 8A to 8C is implemented as aU-shape-surround-gate-FINFET. FIG. 8A shows a vertical cross sectionalview of the second transistor 3 _(i) in a first vertical section planeE-E, FIG. 8B shows a horizontal cross sectional view of the secondtransistor 3 _(i) in a horizontal section plane D-D, and FIG. 8C shows avertical cross sectional view in a second vertical section plane F-Fshown in FIG. 8B. The first vertical section plane E-E extendsperpendicular to the top surface 133 of the semiconductor fin 130 and ina longitudinal direction of the semiconductor fin 130, the horizontalsection plane D-D extends parallel to the top surface 133, and thesecond vertical section plane F-F extends perpendicular to the firstvertical section plane E-E. In this transistor, the source region 41 andthe drain region 42 also extend from sidewall 131 to sidewall 132 of thefin-like semiconductor region 130 in the first direction, and arearranged distant to each other in the second direction that isperpendicular to the first direction. In the embodiment illustrated inFIGS. 8A top 8C the second direction corresponds to the longitudinaldirection of the semiconductor fin.

Referring to FIG. 8A, the source region 41 and the drain region 42 areseparated by a trench which extends into the body region 43 from the topsurface 133. The body region 43 is arranged below the source region 41and the drain region 42 in the semiconductor fin 130. The gate electrode44 is arranged adjacent to the body region 43 in the trench and alongthe sidewalls 131, 132 of the semiconductor fin 130 and isdielectrically insulated from the body region 43 by the gate dielectric45. In an upper region, which is a region in which the gate electrode 44is not arranged adjacent to the body region 43, the trench can be filledwith a dielectric material 46.

The second transistor of FIGS. 8A to 8C is, for example, implemented asa depletion transistor, such as an n-type depletion transistor. In thiscase, the source and drain regions 41, 42 and the body region 43 havethe same doping type, wherein the body region 43 usually has a lowerdoping concentration than the source and drain regions 41, 42. In orderto be able to completely interrupt a conducting channel in the bodyregion 43 between the source region 41 and the drain region 42, the gateelectrode 44 along the sidewalls 131, 132 of the fin-like semiconductorregion 130 completely extends along this semiconductor section 130 inthe second direction. In the vertical direction the gate electrode 44along the sidewalls 131, 132 extends from the source and drain regions41, 42 to at least below the trench. According to one embodiment (notshown) the gate electrode 44 extends to the drift region 2.

Implementing the FINFETs illustrated in FIGS. 7A to 7C and 8A to 8C asU-shape-surround-gate-FINFET in which the gate electrode 44 has aU-shape and is arranged on sidewalls 131, 132 and on a top surface 133of the semiconductor fin 130 is only an example. These FINFETs couldalso be modified (not illustrated) to have the gate electrode 44implemented with two gate electrode sections arranged on the sidewalls131, 132 but not on the top surface 133 of the semiconductor fin 130. AFINFET of this type can be referred to as double-gate FINFET. Each ofthe FINFETs explained above and below can be implemented asU-shape-surround-gate-FINFET or as double-gate FINFET. It is evenpossible to implement different types of FINFETs in one integratedcircuit.

FIG. 9 illustrates a vertical cross section through a transistorarrangement in which the second transistors are implemented as FINFETswith a topology as illustrated in FIGS. 8A and 8B. FIG. 9 illustrates across section through the fin-like semiconductor region in which thesource and drain regions of the individual second transistors 3 ₀-3 _(n)are arranged. The source and drain regions as well as the body regionsof neighboring second transistors are insulated from each other bydielectric layers 47 which extend in a vertical direction of the fin inwhich the source and drain regions of the second transistors areimplemented.

In the embodiment of FIG. 9 the first transistor is also implemented asa FINFET. In this transistor the source region 11 and the drift region 2are separated by the body region 12. The gate electrode 13 that isarranged in the trench and the position of which at the sidewalls of thesemiconductor fin is illustrated by dotted lines, extends from thesource region 11 across the body region 12 to the drift region 2. Thesource terminal S electrically contacts the source region ii and thebody region 12 at the top surface of the semiconductor fin of the firsttransistor 6. The source region 11 and the body region 12 of the firsttransistor are insulated from the active semiconductor regions of afirst one 3 ₀ of the second transistors by a dielectric layer 48.

In the embodiment illustrated in FIG. 9, the drift region can beimplemented as a substrate on which the semiconductor fins of the firsttransistor 1 and the second transistors 3 ₀-3 _(n) are arranged.According to another embodiment illustrated in dashed and dotted linesin FIG. 9, the drift region 2 in a lateral direction extends from belowthe body region 12 of the first transistor 1 to the drain zone 15, andadjoins a semiconductor layer 2′ that is doped complementary. This layer2′ may extend to the body region 12 of the first transistor adjacent tothe drift region 2 or may be connected to source potential, which is theelectrical potential of the source region 11, at a position notillustrated in FIG. 9.

In the embodiment illustrated in FIG. 9, the first transistor 1 and thesecond transistors 3 ₀-3 _(n) are implemented in one semiconductor fin,with the individual transistor being in line in a longitudinal directionof the semiconductor fin. The first transistor 1 and the secondtransistors connected in series 3 ₀-3 _(n) may each include a number oftransistor cells connected in parallel. This will be explained withreference to FIG. 10.

FIG. 10 shows a top view of an arrangement with second transistors 3_(n−3), 3 _(n−2), 3 _(n−1), 3 _(n), wherein each of these transistorshas a plurality of transistor cells which, for a transistor 3 _(n−3),are denoted as 3 _(1,n−3), . . . , 3 _(m,n−3) in FIG. 10. Each of thesetransistor cells, such as transistor cell 3 _(1,n−3) is implemented as aFINFET with one of the topologies as explained before. The individualtransistor cells of one transistor, such as transistor 3 _(n−3) have acommon gate electrode 44 which—in a manner not illustrated—iselectrically connected to the source terminal of a neighboring secondtransistor. In FIG. 10, besides the arrangement with the plurality ofsecond transistors only the drain region 15 the source region 11 areschematically illustrated. The second transistors 3 _(n−3)-3 _(n)illustrated in FIG. 10 are transistors arranged close to the drainregion 15, wherein the second transistor 3 _(n) is the second transistorwhich has its drain regions electrically connected to the drain region15 of the first transistor. Electrical connections between the sourceand drain regions of the individual second transistors are illustratedby bold lines in FIG. 10. These electrical connections can beimplemented using conventional techniques for electrically connectingsemiconductor devices in an integrated circuit, such as conventionalwiring arrangements.

In the embodiment illustrated in FIG. 10, the source and drain regionsof the individual transistor cells are arranged distant to each other inthe current flow direction of the first transistor. The current flowdirection is a direction from the drain region 15 to the source region11.

FIG. 11 illustrates a top view on a further embodiment of a secondtransistor arrangement. In this embodiment source and drain regions 41,42 of the transistor cells of one second transistor 3 _(n−2), 3 _(n−1),3 _(n) are arranged distant in a direction perpendicular to the currentflow direction. In this direction perpendicular to the current flowdirection source and drain regions of the individual transistor cellsare arranged alternatingly, so that two transistor cells that areadjacent in the direction perpendicular to the current flow directionhave a common source region 41 and two transistor cells that areadjacent in the direction perpendicular to the current flow directionhave a common drain region 42. The source regions 41 of one secondtransistor, such as transistor 3 _(n−2), are electrically connected withthe drain regions 42 of a neighboring transistor, such as transistor 3_(n−1). The individual transistor cells of one transistor have a commongate electrode 44. The gate electrode of one second transistor iselectrically connected to the source region of a neighboring secondtransistor in a manner as explained in detail hereinbefore.

In FIGS. 10 and 11, which show top views of a section of an arrangementwith second transistors, the semiconductor fins of the individualtransistor cells are out of view. For two transistor cells and for twogroups of transistor cells, respectively, the position of thesemiconductor fins 130 is illustrated in dotted lines. In the embodimentillustrated in FIG. 9, the longitudinal directions corresponds to thecurrent flow direction, while in the embodiment of FIG. 10, thelongitudinal directions of the semiconductor fins run perpendicular tothe current flow direction. The space between the semiconductor fins canbe filled with gate electrode material, so as to form one contiguousgate electrode 44 for each second transistor 3 _(n−2-), 3 _(n−2), 3_(n).

The active regions of the first transistor and the active regions of thesecond transistors can have conventional doping concentrations. In thefirst transistor 1, the doping concentration of the source and drainregions 11, 15 is, e.g., in the range of between 10¹⁹ cm⁻³ and 10²¹cm⁻³, the doping concentration of the body region 12 is, e.g., in therange of between 10¹⁵ cm⁻³ and 10¹⁹ cm⁻³, and the doping concentrationof the drift region 2 is, e.g., in the range of between 10¹³ cm⁻³ and10¹⁸ cm⁻³. In the second transistors 3 ₁-3 _(n), the dopingconcentration of the source and drain regions 41, 42 is, e.g., in therange of between 10¹⁹ cm⁻³ and 1021 cm⁻³, and the doping concentrationof the body region 12 is, e.g., in the range of between 10¹⁷ cm⁻³ and10²⁰ cm⁻³.

FIG. 12 illustrates a further embodiment of a transistor arrangement inwhich the second transistors 3 ₁-3 _(n) are implemented as MOSFET, inparticular as depletion MOSFET. Unlike the arrangement illustrated inFIG. 1, the second transistors of the arrangement of FIG. 12 are coupledto the drift region of the first transistor 1 via their bulk/bodyterminals instead of their source terminals. However, the secondtransistors 3 ₁-3 _(n) have their load paths connected in series, andthe gate terminal of one second transistor is connected to the sourceterminal of a neighbouring second transistor, wherein the secondtransistor 3 ₁ that has its load path directly connected to the loadpath of the first transistor, has its gate terminal connected to thesource terminal of the first transistor 1.

FIG. 13 illustrates a further embodiment of a transistor arrangement.This transistor arrangement includes a first transistor 6 and anarrangement (second transistor arrangement) 3 with a plurality of secondtransistors 3 ₀-3 _(n). The first transistor 6 has a load path between afirst and a second load terminal and a control terminal, and each of thesecond transistors has a load path between a first and a second loadterminal and a control terminal. The second transistors 3 ₀-3 _(n) havetheir load paths connected in series between first and second terminals3 ₁, 3 ₂, wherein a series circuit with the load paths of the secondtransistors 3 ₀-3 _(n) is connected in series with the load path of thefirst transistor 1. The first transistor 6 can be a power transistorwith a drift zone (not illustrated) but could also be a low-voltagetransistor without a drift region.

Each of the second transistors 3 ₀-3 _(n) has its control terminalconnected to the load terminal of another one of the second transistors3 ₀-3 _(n) or to one of the load terminals of the first transistor 6. Inthe embodiment illustrated in FIG. 13 a first one 3 ₀ of the secondtransistors which is adjacent to the first transistor 6 so that it hasits load path directly connected to the load path of the firsttransistor 6 has its control terminal connected to a first load terminalof the first transistor 6. The other second transistors, which aretransistors 3 ₁-3 _(n) in the embodiment illustrated in FIG. 13, havetheir control terminals connected to the first load terminal of theadjacent second transistor. The connection of the control terminals ofthe second transistors to the load terminals of the first transistor 1or to the load terminals of another one of the second transistors issuch that the first one 3 ₀ of the second transistors has a drivevoltage which corresponds to the voltage across the load path of thefirst transistor 6, and such that the drive voltages of the other secondtransistors correspond to the voltage across the load path of anadjacent second transistor.

In the embodiment illustrated in FIG. 13, the first transistor 6 and thesecond transistors 3 ₀-3 _(n) are MOSFET which each have a gate terminalthat forms a control terminal, and a drain and source terminal, whereinthe drain and source terminals form load path terminals. The first one 3₀ of the second transistors has its gate terminal connected to thesource terminal of the first transistor, and the other secondtransistors 3 ₁-3 _(n) have their gate terminals connected to the sourceterminal of an adjacent one of the second transistors. The firsttransistor 1 is an enhancement MOSFET, such as an n-type enhancementMOSFET, and the second transistors 3 ₀-3 _(n) are depletion MOSFET, suchas n-type depletion MOSFETs, in this embodiment. However, the circuit isnot restricted to be implemented with n-type transistors but may beimplemented with p-type transistors as well.

The transistor arrangement with the first transistor 1 and a secondtransistor 3 ₀-3 _(n) can be switched on and off like a conventionaltransistor by applying a suitable drive voltage to the first transistor6. The operating principle will now shortly be explained: Assume thatthe arrangement is first in its on-state, so that the first transistor 1and the second transistors are conducting and the first transistor 1 isswitched off. In this case, a voltage drop across the load path of thefirst transistor 1 increases, thereby switching off the first one 3 ₀ ofthe second transistors. When this second transistor is switched off, thevoltage drop across its load path increases so that a second one 3 ₁ ofthe second transistors is switched off, which in turn switches a thirdone 3 ₂ of the second transistors off, etc. This continues until all ofthe second transistors 3 ₀-3 _(n) are switched off.

When the arrangement is in its off-state and the first transistor isswitched on, a decreasing voltage drop across the load path of the firsttransistor 1 switches the first one 3 ₀ of the second transistors on,which in turn switches the second one of the second transistors 3 ₁ on,etc. This continues until all of the second transistors 3 ₀-3 _(n) areswitched on.

The switching states of the second transistors 3 ₀-3 _(n) connected inseries with the first transistor 6 are dependent on the switching stateof the first transistor 6, where the arrangement with the secondtransistors 3 ₀-3 _(n) has a high resistance when the first transistorsis switched off and has a low resistance when the first transistor 6 isswitched on. In the following, the arrangement with the secondtransistors will be referred to as active drift region, where theterminal 31 that corresponds to a drain terminal of the secondtransistor 3 _(n) will be referred to as drain terminal D₃ of the activedrift region 3.

The voltage blocking capability of the overall transistor arrangementis, however, higher than the voltage blocking capability of only thefirst transistor 6. In its on-state, the transistor arrangement behaveslike a series circuit of resistors, which is illustrated in FIG. 14A.The individual resistors R1 and R3 ₀-R3 _(n) each represent theon-resistances of the individual transistors connected in series. In theoff-state the transistor arrangement behaves like a series circuit withcapacitors C3 ₀-C3 _(n), wherein each of the capacitors represents thegate-source-capacitance of one of the transistors connected in series.The capacitor C1 _(DS) connected in parallel with thegate-source-capacitance C3 ₀ of the first one of the second transistorsrepresents the drain-source-capacitance of the first transistor 1. Thecapacitor C3 _(nDS) connected between the gate-source-capacitance C3_(n) of the second transistor 3 _(n) represents thedrain-source-capacitance of the second transistor 3 _(n). Thedrain-source-capacitances of the other second transistors are notexplicitly shown in FIG. 14B.

In the embodiment illustrated in FIG. 13, the first transistor 6 is anormally-off (enhancement) transistor, while the second transistor 3 ₀-3_(n) are normally-on (depletion) transistors. However, this is only anexample. Each of the first transistor and the second transistors can beimplemented as a normally-on transistor or as a normally-off transistor.Furthermore, the individual transistors can be implemented as n-typetransistors or p-type transistors.

Further, any type of transistor can be used to implement the firsttransistor 1 and the second transistors 3 ₀-3 _(n), like a MOSFET, aMISFET, a MESFET, an IGBT, a JFET, a FINFET, a nanotube device, or anHEMT, etc. FIG. 15 illustrates an embodiment in which the firsttransistor 6 is an (n-type) enhancement transistor while the secondtransistors are n-type JFET. Of course, the arrangement could also beimplemented with p-type transistors as the first transistor 6 and thesecond transistors 3 ₀-3 _(n). FIG. 16 illustrates an embodiment inwhich the first transistor 6 is an (n-type) enhancement transistor whilethe second transistors are nanotube devices or HEMTs.

The operating principle of the semiconductor arrangement is explained inthe following. Just for explanation purposes it is assumed that thefirst semiconductor device 6 is implemented as an n-type enhancementMOSFET, that the second transistors 3 ₀-3 _(n) are implemented as n-typedepletion MOSFETs or n-type JFETs, and that the individual devices 2, 3_(i) are interconnected as illustrated in FIG. 1. The basic operatingprinciple, however, also applies to semiconductor device arrangementsimplemented with other types of first and second semiconductor devices.

It is commonly known that depletion MOSFETs or JFETs, that can be usedto implement the second transistors 3 _(i), are semiconductor devicesthat are in an on-state when a drive voltage (gate-source voltage) ofabout zero is applied, while MOSFETs or JFETs are in an off-state whenthe absolute value of the drive voltage is higher than a pinch-offvoltage of the device. The “drive voltage” is the voltage between thegate terminal and the source terminal of the device. In an n-type MOSFETor JFET the pinch-off voltage is a negative voltage, while the pinch-offvoltage is a positive voltage in a p-type MOSFET or JFET.

When a (positive) voltage is applied between the first terminal 31 ofthe second transistor arrangement 3 and a first load terminal (sourceterminal) S of the first semiconductor device 6 (which can be referredto as first and second external terminals) and when the firstsemiconductor device 6 is switched on by applying a suitable drivepotential to the control terminal G, the 1st second transistor 3 ₀ isconducting (in an on-state), the absolute value of the voltage acrossthe load path (drain-source path) D-S of the first semiconductor device6 is too low so as to pinch-off the 1st second transistor 3 ₀.Consequently, the 2nd second transistor 3 ₁ controlled by the load pathvoltage of the 1st second transistor 3 ₀ is also starting to conduct,etc. In other words, the first semiconductor device 6 and each of thesecond transistors 3 _(i) are finally conducting so that thesemiconductor arrangement is in an on-state. When the semiconductorarrangement 1 is in an on-state and when the first semiconductor device6 is switched off, the voltage drop across the load path of the firstsemiconductor device 6 increases, so that the 1st second transistor 3 ₀starts to switch off when the absolute value of the load-path voltage ofthe first semiconductor device 6 reaches the pinch-off voltage of the1st second transistor 3 ₀. When a positive voltage is applied betweenthe first and second external terminals 31, S, the voltage between thesecond load terminal (drain terminal) D and the first load terminal S ofthe first semiconductor device 6 is also a positive voltage when thefirst semiconductor device 6 switches off. In this case, the gate-sourcevoltage of the 1st second transistor 3 ₀ is a negative voltage suitableto pinch off this transistor 3 ₀.

When the 1st second transistor 3 ₀ is switched off, the voltage dropacross its load path increases so that the 2nd second transistor 3 ₁ isswitched off, which in turn switches off the 3rd second transistor 3 ₂,and so on, until each of the second transistors 3 _(i) is switched offand the semiconductor device arrangement is finally in a stableoff-state. The external voltage applied between the first and secondexternal terminals 31, S switches as many 2nd transistors from theon-state to the off-state as required to distribute the external voltageover the first semiconductor device 6 and the second transistors 3 _(i).When applying a low external voltage, some second transistor are stillin the on-state, while others are in the off-state. The number of secondtransistors 3 _(i) that are in the off-state increases as the externalvoltage increases. Thus, when a high external voltage is applied, thatis in the range of the voltage blocking capability of the overallsemiconductor device arrangement, the first semiconductor device andeach of the second transistors are in the off-state.

When the semiconductor device arrangement with the first semiconductordevice 6 and the second transistors 3 _(i) is in an off-state and whenthe first semiconductor device 6 is switched on, the voltage drop acrossthe load path of the first semiconductor device 6 decreases so that itswitches on the 1st second transistor 3 ₀, which in turn switches on the2nd second transistor 3 ₁, and so on. This continues until each of thesecond transistors 3 _(i) is again switched on.

The switching states of the second transistors 3 _(i) connected inseries with the first semiconductor device 6 are dependent on theswitching state of the first semiconductor device 6 and follow theswitching state of the first semiconductor device 6. Thus, the switchingstate of the overall semiconductor device arrangement is defined by theswitching state of the first semiconductor device 6. The semiconductordevice arrangement is in an on-state when the first semiconductor device6 is in an on-state, and the semiconductor device arrangement is in anoff-state when the first semiconductor device 6 is in an off-state.

The semiconductor device arrangement has a low resistance between thefirst and second external terminals 31, S, and has a high resistancebetween the first and second external terminals 31, S when it is in anoff-state. In the on-state, an ohmic resistance between the first andsecond external terminals 31, S corresponds to the sum of theon-resistances RON of the first semiconductor device 6 and the secondtransistors 3 _(i). A voltage blocking capability (which is the maximumvoltage that can be applied between the first and second externalterminals 31, S when the semiconductor arrangement is in an off-statebefore an Avalanche breakthrough sets in) corresponds to the sum of thevoltage blocking capabilities of the first semiconductor device 6 andthe second transistors 3 _(i). The first semiconductor device 6 and theindividual second transistors 3 _(i) may have relatively low voltageblocking capabilities, such as voltage blocking capabilities of between3V and 50V. However, dependent on the number n of second transistors 3 ahigh overall voltage blocking capability of up to several 100V, such as600V or more, can be obtained.

The voltage blocking capability and the on-resistance of thesemiconductor device arrangement are defined by the voltage blockingcapabilities of the first semiconductor device 6 and the secondtransistors 3 _(i) and by the on-resistances of the first semiconductordevice 6 and the second transistors 3 _(i), respectively. Whensignificantly more than two second transistors 3 _(i) are implemented(n>>2), such as more than 5, more than 10, or even more than 20 secondtransistors 3 _(i) are implemented, the voltage blocking capability andthe on-resistance of the semiconductor arrangement are mainly defined bythe arrangement 3 with the second transistors 3 _(i). The overallsemiconductor device arrangement 1 can be operated like a conventionalpower transistor, where in a conventional power transistor, anintegrated drift region mainly defines the on-resistance and the voltageblocking capability. Thus, the arrangement 3 with the second transistors3 _(i) has a function that is equivalent to the drift region in aconventional power transistor. The arrangement 3 with the secondtransistors 3 _(i) can, therefore, be referred to as active drift region(ADR). The overall semiconductor device arrangements of FIG. 13, butalso the semiconductor device arrangement of FIG. 1 that has an activedrift region connected in parallel with the drift region of a powertransistor 1, can be referred to as ADR transistor, or as ADRFET, whenthe first semiconductor device is implemented as a MOSFET.

Like the circuit arrangement illustrated in FIG. 1 that has the secondtransistors 3 ₀-3 _(n) connected in parallel with the drift region 2 ₀-2_(n) of the power transistor 1, the circuit arrangement illustrated inFIG. 13 that has the second transistors 3 ₀-3 _(n) connected in serieswith the load path D-S of the first transistor 6 can be implemented inone semiconductor body. FIG. 17 illustrates a first embodiment of asemiconductor body 100, in which a circuit arrangement with a firsttransistor 6 and a plurality of second transistors 3 ₀-3 _(n) areintegrated. Specifically, FIG. 17 illustrates a vertical cross sectionalview of a semiconductor fin in which active regions (source, drain andbody regions) of a first semiconductor device 6 and of n+1 secondtransistors 3 ₀-3 _(n) are arranged.

The embodiment illustrated in FIG. 17 is based on the embodimentillustrated in FIG. 9. In the circuit arrangement or integrated circuitillustrated in FIG. 17, the first transistor 6 and each of the secondtransistors 3 ₀-3 _(n) are implemented as FINFETs, specifically asU-trench surround-gate FINFETs. FIG. 17 illustrates a vertical crosssectional view of the semiconductor body 100 in a vertical section planethat extends through the semiconductor fins of the individual FINFETs inthe longitudinal direction of the individual semiconductor fins. Thesecond transistors 3 ₀-3 _(n) are implemented as explained withreference to FIGS. 8A to 8C herein before, with the difference, thatbody regions 43 of the individual FINFETs are not arranged above thedrift region (2 in FIGS. 8A to 8C) of a power transistor, but arearranged on a substrate 7. This substrate 7 can be implemented in anumber of different ways as will be explained with reference to FIGS. 18and 19 below. The individual second transistors 3 ₀-3 _(n) can beidentical; in FIG. 17 reference characters for only one of the pluralityof second transistors, namely for the transistor 3 ₁ are indicated.

The first transistor 6, like the second transistors 3 ₀-3 _(n), is alsoimplemented as a U-trench surround-gate FINFET in the embodimentillustrated in FIG. 17. However, the first transistor 6 as well as thesecond transistors 3 ₀-3 _(n) could be implemented as double-gateFINFETs as well. It is even possible, to implement the first transistor6 and the second transistors 3 ₀-3 _(n) as different types oftransistors.

Referring to FIG. 17, a source region 61 and a drain region 62 of thefirst transistor 6 are arranged distant to each other in a longitudinaldirection of the semiconductor fin, where the source and drain regions61, 62 are separated by the U-trench, which from a top surface of thesemiconductor fin of the first transistor 6 extends into thesemiconductor fin. In the U-trench and along the sidewalls (not shown inFIG. 17) of the semiconductor fin a gate electrode 64 and a gatedielectric 65 are arranged, so that the gate electrode 65 is adjacent toa body region 63 of the first transistor 6, wherein the body region 63is arranged below the source and drain regions 61, 62 and also below theU-trench. The position of the gate electrode 64 and the gate dielectric65 along one sidewall of the semiconductor fin is indicated in dottedline for the first transistor 6 as well as for the second transistors 3₀-3 _(n) in FIG. 17.

The first transistor 6 is, for example, implemented as an enhancementtransistor. In this case, the source region 61 and the drain region 62have a first doping type, such as, for example, an n-type, and the bodyregion 63 has a second doping type, such as, for example, a p-type. Thesource region 61 and the body region 63 are both connected to the sourceterminal S, which is only schematically illustrated in FIG. 17. In theintegrated circuit according to FIG. 17, the first transistor 6 and thesecond transistors 3 ₀-3 _(n) are arranged such that longitudinaldirections of the semiconductor fins of the individual transistors arein-line, so that a first one 3 ₀ of the second transistors adjoins thefirst transistor 6 in a direction corresponding to a longitudinaldirection of the semiconductor fin of the first transistor 1, a secondone 3 ₁ of the second transistors adjoins the first one 3 ₀ of thesecond transistor in a direction corresponding to the longitudinaldirection of the semiconductor fin of the first one 3 ₀ of the secondtransistors, etc. The semiconductor fins of the individual secondtransistors 3 ₀, 3 _(n) are insulated from each other by insulationlayers 47 extending from the top surface of the semiconductor finsthrough the semiconductor fin down to the substrate 7. The semiconductorfin including the active transistor regions of the first transistor 6 isinsulated from the semiconductor fin including the active transistorregions of the first one 3 ₀ of the second transistors by a furtherinsulation layer 48 extending from the top surface of the semiconductorfin down to the substrate 7. The drain region of the first transistor 6is located at a first longitudinal end of the semiconductor fin of thefirst transistor 6, wherein the first longitudinal end is thelongitudinal end that faces towards the semiconductor fin of the firstone 3 ₀ of the second transistors. The source region 61 of the firsttransistor 6 is arranged at a second longitudinal end of thesemiconductor fin of the first transistor 6, where the secondlongitudinal end faces away from the semiconductor fin of the first one3 ₀ of the second transistors. At this second longitudinal end, the bodyregion 63 extends to the top surface of the semiconductor fin and isconnected to the source terminal S at this top surface. However, this isonly an example. The source terminal could also include a contactelectrode extending through the source region 61 into the body region 63and connecting both, the source region 61 and the body region 63.

Like in FIG. 13, D₃ in FIG. 17 denotes a drain terminal of the circuitarrangement that is formed by a drain terminal of a last one 3 _(n) ofthe second transistors in the chain of second transistors 3 ₀-3 _(n). Inthe embodiment illustrated in FIG. 17, a first semiconductor region 33of the same doping type as the drain region 42 of the second transistor3 _(n) adjoins the drain region 42 of the second transistor 3 _(n) andis connected to the drain terminal D₃. This drain terminal D₃ is thedrain terminal of the active drift region.

According to one embodiment, the first transistor 6 is implemented as ann-type enhancement transistor, while the second transistors 3 ₀-3 _(n)are implemented as n-type depletion transistors. A gate electrode of thefirst one 3 ₀ of the second transistors is electrically connected to thesource terminal S of the first transistor 6, and the source region ofthis first one 3 ₀ of the second transistor is electrically connected tothe drain region 62 of the first transistor 6. From the other secondtransistors 3 ₁-3 _(n) each one has its gate terminal connected to thesource terminal of a neighboring second transistor arranged in thedirection of the first transistor 6 and has its source terminalconnected to the drain terminal of this neighboring second transistor.For example, the second transistor 3 ₂ has its gate electrode connectedto the source terminal of second transistor 3 ₁ and has source terminalconnected to the drain terminal or drain region of the second transistor3 ₁.

In the same way as explained with reference to FIGS. 10 and 11, each ofthe second transistors 3 ₀-3 _(n) may include a plurality of transistorcells connected in parallel. Longitudinal directions of thesemiconductor fins of the individual transistor cells of two neighboringsecond transistors may be arranged in line, as illustrated in FIG. 10.However, it is also possible for the longitudinal directions of thesemiconductor fins of two neighboring second transistors, such as, forexample, the transistors 3 _(n−1) and 3 _(n) of FIG. 11 to be arrangedin parallel with each other.

Referring to FIG. 17, the substrate 7 can be implemented as asemiconductor substrate of a doping type complementary to the dopingtype of the body regions 43 of the second transistors 3 ₀-3 _(n). Thesubstrate 7 is arranged below the first transistor 6 and each of thesecond transistors 3 ₀-3 _(n) and may adjoin the body region 63 of thefirst transistor 6 as well as the body region 43 of the secondtransistors 3 ₀-3 _(n).

FIG. 18 illustrates a further embodiment of an integrated circuitincluding a first transistor 6 and a plurality of second transistors 3₀-3 _(n). The integrated circuit of FIG. 18 is a modification of theintegrated circuit of FIG. 17, wherein in the integrated circuitaccording to FIG. 18 a substrate 7 includes a first section 71 of adoping type complementary to the doping type of the body regions 43 ofthe second transistors 3 ₀-3 _(n). This first section 71 is arrangedbelow the body regions 43 of the second transistors 3 ₀-3 _(n) and alsobelow the insulation layers 47, so as to form a continuous semiconductorregion 71 that extends in a lateral or horizontal direction of thesemiconductor body 100. The first section 71 of the substrate 7 does notextend below the first transistor 6, where the further insulation layer48 extends deeper into the semiconductor body 100 than the insulationlayer 47, so as to separate the first section 71 from those regions ofthe semiconductor body 100 in which the first transistor 6 isimplemented. The substrate 7 further includes a second section 72 dopedcomplementarily to the first section 71, wherein this second section 72adjoins the body region 63 of the first transistor 6 and extends inlateral or horizontal direction of the semiconductor body 100 below thefirst transistor 6 and each of the second transistors 3 ₀-3 _(n).

The first and second sections 71, 72 of the substrate 7 provide ajunction isolation between the second transistors 3 ₀-3 _(n) and thefirst transistor 6. Further, the first section 71 of the substrate 7 andthe body regions 43 provide a junction insulation between the secondtransistors 3 ₀-3 _(n). In the embodiment illustrated in FIG. 18, theinsulation layer 48 separating the first transistor 6 and a first one 3₀ of the second transistors 3 ₀-3 _(n) extends form a first surface ofthe semiconductor body 100 into the semiconductor body 100 and into thesecond substrate section 72. This insulation layer 48 may extend deeperinto the semiconductor body 100 than the insulation layers 47 separatingthe individual second transistors 3 ₀-3 _(n).

According to a further embodiment (not illustrated) the insulation layer48 extends through the second substrate section 72 in a verticaldirection of the semiconductor body 100 to a second surface of thesemiconductor body 100 opposite the first surface.

The insulation layers 47, 48 may completely be comprised of a dielectricmaterial. However, according to a further embodiment, the insulationlayers include a dielectric material along sidewalls and a bottom oftrenches in which the insulation layers are formed, and an electricallyconducting material, such as a metal or a polysilicon, filling thetrenches.

According to a further embodiment, the first substrate section 71 ofFIG. 18 has the same doping type as the body regions 43 of the secondtransistors 3 ₀-3 _(n) and the second substrate section 72 is dopedcomplementarily to the first substrate section 71 and the body regions.

FIG. 19 illustrates a further embodiment of an integrated circuit. Inthis embodiment, the substrate 7 is implemented as an SOI-substrate andincludes an insulation layer 73 adjoining the body regions 43 of thesecond transistors 3 ₀-3 _(n) and the body region 63 of the firsttransistor 6 and extending in a lateral or horizontal direction of thesemiconductor body 100. The insulation layer 73 is arranged on asemiconductor substrate 74 of a first or a second doping type.

Each of the first semiconductor device 6 and the second transistors 3(referred to as devices in the following) may include a plurality ofidentical cells (transistor cells) that are connected in parallel. Eachof these cells can be implemented as FINFET. Providing a plurality ofcells connected in parallel in one device can help to increase thecurrent bearing capability and to reduce the on-resistance of theindividual device.

FIG. 20 illustrates a top view on a semiconductor arrangement accordingto a first embodiment which includes a first semiconductor device 6 anda plurality of second transistors 3 _(i), with each of these deviceshaving a plurality (from which three are illustrated) cells connected inparallel. The individual cells of one device are implemented indifferent semiconductor fins 130 _(I), 130 _(II), 130 _(III). Each ofthese cells has a source region 61, 41 _(i) that is additionally labeledwith “S” in FIG. 19, and a drain region 62, 42 _(i) that is additionallylabeled with “D” in FIG. 20. The cells of one device are connected inparallel by having the source regions of the one device connectedtogether and by having the drain regions of the one device connectedtogether. These connections as well as connections between the loadterminals of the different devices are schematically illustrated in boldlines in FIG. 20. Connections between the control terminals (gateterminals) and the load terminals of the different devices are notillustrated in FIG. 20. The connections between the cells and thedifferent devices can be implemented using conventional wiringarrangements arranged above the semiconductor body and contacting theindividual active regions (source and drain regions) through vias. Thosewiring arrangements are commonly known so that no further explanationsare required in this regard. The individual cells of one device 6, 3 ₀,3 ₁, 3 ₂, 3 _(n) have a common gate electrode 64, 44 ₀, 44 ₁, 44 ₂, 44_(n) arranged in the U-shaped trenches of the individual semiconductorfins and in trenches between the individual fins. These “trenchesbetween the fins” are longitudinal trenches along the fins 130 _(I), 130_(II), 130 _(III).

FIG. 21 illustrates a further embodiment for implementing one secondtransistor 3 _(i) with a plurality of transistor cells. In thisembodiment, a plurality of transistor cells of the second transistor 3_(i) are implemented in one semiconductor fin 130. In the longitudinaldirection of the semiconductor fin 130, source and drain regions 41_(i), 42 _(i) are arranged alternately with a source region 41 _(i) anda neighboring drain region 42 _(i) being separated by one (U-shaped)trench that accommodates the gate electrode 44 _(i). The source regions41 _(i) are connected to the first load terminal (source terminal) S ofthe second transistor 3 _(i), and the drain regions 42 _(i) areconnected to the second load terminal (drain terminal) D of the secondtransistor 3 _(i), so that the individual transistor cells are connectedin parallel. The gate electrode 44 is common to the individualtransistor cells and extends along the sidewalls of the semiconductorfin 130 in the longitudinal direction. Each source region 41 and eachdrain region 42 (except for the source and drain regions arranged at thelongitudinal ends of the semiconductor fin 130) is common to twoneighboring transistor cells.

The concept of providing several transistor cells in one semiconductorfin explained with reference to FIG. 21 is, of course, also applicableto the implementation of the first semiconductor device 6.

Referring to FIGS. 22A to 22C, one second transistor 3 _(i) may includea plurality of semiconductor fins 130 _(IV), 130 _(V), 130 _(VI), 130_(VII), with each semiconductor fin 130 _(IV)-130 _(VII) including aplurality of transistor cells (one of these cells is highlighted by adashed and dotted frame in FIG. 22A). FIG. 22A shows a top view of onesecond transistor 3 _(i), FIG. 22B shows a vertical cross sectional viewin a section plane F-F cutting through source regions in different fins130 _(IV)-130 _(VII), and FIG. 22C shows a vertical cross sectional viewin a section plane G-G cutting through the trenches with the gateelectrode 44 in different fins. Referring to FIG. 22A, the sourceregions 41 _(i) of the individual transistor cells are connected to thefirst load terminal S and the drain regions of the individual transistorcells are connected to the second load terminal D of the secondtransistor 3 _(i) so that the individual transistor cells are connectedin parallel. These connections are only schematically illustrated inFIG. 22A.

The concept of providing a plurality of semiconductor fins with eachsemiconductor fin including a plurality of transistor cells explainedwith reference to FIGS. 22A to 22C is, of course, also applicable to theimplementation of the first semiconductor device 6.

Although only 20 transistor cells are illustrated in FIG. 22A, namelyfive cells in each of the four semiconductor fins 130 _(IV)-130 _(VII),one second transistor 3 _(i) or the first semiconductor device 6 mayinclude up to several thousand or even up to several ten or severalhundred million transistor cells connected in parallel. The individualtransistor cells form a matrix of transistor cells that are connected inparallel. A device (first semiconductor device 6 or second transistor 3_(i)) having a plurality of transistor cells arranged in a matrix willbe referred to as matrix device in the following.

FIG. 22 illustrates how second transistors implemented as matrix devicescan be connected in series. For illustration purposes, only two secondtransistors 3 _(i), 3 _(i+1) are shown in FIG. 23. For connecting thesetwo transistors in series, the source regions of the second transistor 3_(i) are connected to the drain regions of the transistor 3 _(i+1). Thedrain regions of the second transistor 3 _(i) are connected to thesource regions of second transistors 3 _(i−1) (not illustrated), and thesource regions of the second transistor 3 _(i+1) are connected to thedrain regions of second transistors 3 _(i+2) (not illustrated).

Referring to the explanation provided herein before, the secondtransistors 3 ₀-3 _(n) can be implemented as depletion transistors.These depletion transistors are unipolar transistors in which in theon-state minority charge carriers flow. In an n-type depletiontransistor, the majority charge carriers are electrons, while in ap-type charge carrier the majority charge carriers are holes.

However, there can be operation modes or operation scenarios of thecircuit arrangement in which minority charge carriers are generated inthe second transistors 3 ₀-3 _(n). These minority charge carriers can begenerated, for example, by thermal generation, by avalanche generationor when the circuit arrangement is operated in a reverse mode. Circuitarrangements as illustrated in FIGS. 13 to 19 are operated in thereverse mode when a voltage applied between the source terminal S of thefirst transistor 6 and the drain terminal D₃ reverse biases the firsttransistor 6 so that a pn-junction between the source region 61 and thebody region 63 of the first transistor 6 is forward biased. In a circuitarrangement in which the first transistor 6 is implemented as an n-typeenhancement transistor and in which the second transistors 3 ₀-3 _(n)are implemented as n-type depletion transistors, a voltage that reversebiases the first transistor 6 is a positive voltage between the sourceterminal S and the drain terminal D₃, while in a circuit arrangementwith p-type transistors a negative voltage between the source terminaland the drain terminal reverse biases the first transistor. In thiscase, the first transistor 6 is operated as a diode (body diode), wherethe current through the first transistor 6 further flows through thesecond transistors 3 ₀-3 _(n) to the drain terminal D₃. When the firsttransistor 6 is reverse biased, minority charge carriers from the firsttransistor 6 will travel through the substrate 7 to the individualsecond transistors 3 ₀-3 _(n), when the substrate is doped complementaryto the body region 63 of the first transistor 6. In an arrangement inwhich the substrate 7 has the same doping type as the body region 63 andis connected to the body region 63, the substrate 7 injects minoritycharge carriers into the body regions 43 of the second transistors 3 ₀-3_(n). However, this is dependent on the type of substrate. When, forexample, an SOI substrate, as illustrated in FIG. 19, is used, atravelling of minority charge carriers from the first transistor 6 tothe second transistors 3 ₀-3 _(n) can be prevented.

Minority charge carriers that are generated in the second transistors 3₀-3 _(n) or that are somehow injected into the second transistors 3 ₀-3_(n) may negatively influence the operation of the second transistors 3₀-3 _(n). These minority charge carriers may accumulate along the gatedielectric 45 and may therefore shield the gate electrode 44, so that ina worse-case scenario the second transistors 3 ₀-3 _(n) cannot beswitched off any more.

In order to prevent problems that may occur in connection with theaccumulation of minority charge carriers in the second transistors 3 ₀-3_(n), the second transistors 3 ₀-3 _(n) may include a semiconductorregion that is doped complementarily to the source, drain and bodyregions of the second transistors 3 ₀-3 _(n) and that is connectedbetween the body region and a source terminal or source electrode of therespective second transistor 3 ₀-3 _(n).

FIGS. 24A and 24B illustrate one embodiment of a second transistor 3_(i) that includes such an additional semiconductor region.

The second transistor 3 _(i) illustrated in FIGS. 24A and 24B isimplemented as an U-trench surround-gate FINFET, however, the basicprinciple of providing the additional semiconductor region that is dopedcomplementarily to the active regions of the transistor 3 _(i) can beapplied to any type of second transistor accordingly. FIG. 24Aillustrates a vertical cross sectional view of the second transistor 3_(i) in a vertical section plane extending through the semiconductor finof the transistor 3 _(i) in the longitudinal direction of thesemiconductor fin. FIG. 24B illustrates a horizontal cross sectionalview of the transistor 3 _(i).

Referring to FIGS. 24A and 24B, the transistor 3 _(i) includes a firstsemiconductor region 49 that is doped complementarily to the sourceregion 41, the drain region 42 and the body region 43 of the transistor3 _(i). This first semiconductor region 49 is arranged between the bodyregion 43 and a source electrode 81 of the transistor 3 _(i), where thesource electrode 81 is further connected to the source region 41 . Itshould be noted that each of the second transistors 3 ₀-3 _(n) explainedbefore has a source electrode corresponding to the source electrode 81illustrated in FIG. 24A. However, for the ease of illustration thesesource electrodes are not explicitly shown in the drawings explainedbefore.

Referring to FIG. 24B, the first semiconductor region 49 is arrangedadjacent to the source region 41, wherein both, the source region 41 andthe first semiconductor region 49 are arranged between the body region43 and the source electrode 81. The first semiconductor region 49 allowsminority charge carriers that may be present in the body region 43 toflow to the source electrode 81, so as to be removed from the bodyregion 43. The first semiconductor region 49 therefore helps to preventan accumulation of minority charge carriers in the second transistors 3₀-3 _(n).

FIG. 25 illustrates a further embodiment of a circuit arrangementincluding a first transistor 6 and a plurality of second transistors 3₀-3 _(n) connected in series with the first transistor 6. The circuitarrangement illustrated in FIG. 21 is based on one of the circuitarrangements illustrated in FIGS. 13 to 23. In this embodiment, thefirst transistor 6 is implemented as an enhancement MOSFET, specificallyas an n-type enhancement MOSFET, while the second transistors 3 ₀-3 _(n)are implemented as depletion MOSFETs, specifically as n-type depletionMOSFETs, however, this is only an example. The first and secondtransistors 3 ₀-3 _(n) could also be implemented in any of the otherways explained herein before.

When in the circuit arrangement according to FIG. 25, the firsttransistor 6 is switched off and when a voltage is applied between thedrain terminal D₃ of the active drift region 3 and the source terminal Sof the first transistor 6 with reverse bias condition, the voltage isdistributed such that a part of this voltage drops across the load pathof the first transistor 6, while other parts of this voltage drop acrossthe load paths of the second transistors 3 ₀-3 _(n). However,simulations have shown that there may be no equal distribution of thisvoltage to the second transistors 3 ₀-3 _(n). Instead, those secondtransistors that are arranged closer to the first transistor 6 have ahigher voltage load than those second transistors arranged distant tothe first transistor 6.

In order to more equally distribute the voltage to the secondtransistors, the circuit arrangement of FIG. 25 includes voltagelimiting means 9 that are configured to limit or clamp the voltageacross the second transistors 3 ₀-3 _(n). Optionally, a clamping element9 _(n+1) is also connected in parallel to the load path (between thesource and drain terminals) of the first transistor 6. These voltageclamping means 9 can be implemented in many different ways. Just forillustration purposes the clamping means 9 illustrated in FIG. 25include Zener diodes 9 ₀-9 _(n+1), wherein each Zener diodes 9 ₀-9_(n+1) is connected in parallel with the load path of one of the secondtransistors 3 ₀-3 _(n) and, optionally, the first transistor 6.

Instead of Zener diodes, tunnel diodes, PIN diodes, avalanche diodes, orthe like, may be used as well. According to a further embodiment that isillustrated in FIG. 26, the individual clamping elements 9 ₀-9 _(n+1)are implemented as transistors, such as, for example, p-type MOSFET.Each of these MOSFET has its gate terminal connected to its drainterminal, and the load path (the drain-source path) of each MOSFET isconnected in parallel with the load path of one second transistor 3 ₀-3_(n).

The individual clamping elements, such as the Zener diodes 9 ₀-9 _(n)illustrated in FIG. 25 or the MOSFETs 9 ₀-9 _(n) illustrated in FIG. 26can be integrated in the same semiconductor body as the secondtransistors 3 ₀-3 _(n). However, these clamping elements could also beimplemented as external devices arranged outside the semiconductor body.

Connecting clamping elements parallel to the second transistors 3 ₀-3_(n+1) is not limited to circuit arrangements in which the secondtransistors are connected in series with the first transistor 6.Clamping elements can also be connected in parallel with the secondtransistors 3 ₀-3 _(n) in a circuit arrangement as illustrated in FIG. 1in which the second transistors 3 ₀-3 _(n) are connected in parallel to(sections of) the drift region 2 of a first transistor 1.

Although in the embodiment illustrated in FIG. 25, each secondtransistor 3 ₀-3 _(n) has one clamping element associated thereto, theremay be first and second transistors that do not have a clamping elementassociated thereto. According to one embodiment, only transistors thatare arranged close to the first transistor 6 in the transistor chainwith the first transistor 6 and the second transistor 3 ₀-3 _(n) have aclamping element associated thereto, while transistors that are arrangedmore distant to the first transistor 6 do not have a clamping elementassociated thereto. Further, one clamping element could be associatedwith two or more second transistors connected in series. In this case,one clamping element is connected in parallel with a series circuit oftwo or more second transistors 3 ₀-3 _(n).

Alternatively or additionally to providing clamping elements, such asZener diodes, measures for limiting or clamping the voltage drop acrossone second transistor can be integrated in the first and secondtransistors itself.

FIGS. 27A and 27B illustrate an embodiment of one second transistor 3_(i). This transistor is implemented as U-trench surround-gate FINFET,where FIG. 27A shows a vertical cross sectional view of the transistor 3_(i) and FIG. 27B illustrates a horizontal cross sectional view of thetransistor 3 _(i). This transistor has a source region 41 and a drainregion 42, wherein the source region 41 is electrically connected to asource electrode 81 and the drain region 42 is electrically connected toa drain electrode 82. This transistor 3 _(i) further includes at leastone semiconductor region 91 that is doped complementarily to the drainregion 42, adjoins the body region 43 and is connected to the drainelectrode 82. Optionally, a second semiconductor region 92 that is dopedcomplementarily to the source region 41 adjoins the body region 43 andis connected to the source electrode 81. The first and secondsemiconductor regions 91, 92 adjoin the gate dielectric 45 in regionswhere it is covered by a gate electrode 44. The first and secondsemiconductor regions 91, 92 together with the body region 43 form anenhancement MOSFET of a conduction type complementary to the conductiontype of the second transistor 3 _(i). The enhancement MOSFET is switchedon, when a voltage between the voltage at the gate electrode 44 and thesource region 41 reaches the threshold voltage of this MOSFET, so thatthe voltage drop across the transistor 3 _(i) is clamped to a valueclose to the threshold voltage of this enhancement transistor that iscomplementary to the second transistor 3 _(i).

FIG. 28 illustrates a further embodiment of a second transistor 3 _(i)that includes integrated clamping means. FIG. 28 shows a vertical crosssectional view of this transistor 3 _(i). This transistor 3 _(i)includes an avalanche region 93 of the same doping type as the sourceregion 41, arranged in the body region 43 and adjoining the sourceregion 41. The doping concentration of this avalanche region 93 ishigher than the doping concentration of the body region 43, and maycorrespond to the doping concentration of the source region 41. Startingfrom this avalanche region 93, an avalanche breakthrough sets in inorder to clamp the voltage across the transistor 3 _(i) when the voltagebetween the source and drain regions 41, 42 reaches an avalanche voltagethat is defined by the avalanche region 93.

In the embodiments explained before, the circuit arrangement with thefirst transistor 1, 6 and the second transistor is controlled bycontrolling the first transistor 1, 6, which means by switching on oroff the second transistor 1, 6. Instead of a transistor for controllingthe state of the circuit arrangement, a diode could be used as well.FIG. 29 illustrates a circuit arrangement that is based on the circuitarrangement of FIG. 13 and that includes a diode 60 instead of atransistor. In the embodiment illustrated in FIG. 29, this diode 60 isconnected such that the circuit arrangement blocks (is switched off),when the diode 60 is reverse biased, which is when a positive voltage isapplied between the drain terminal D₃ of the active drift zone, and ananode terminal of the diode 60. This diode can be implemented as anenhancement MOSFET with a floating gate terminal or with a gate terminalconnected to a fixed reference potential, such as ground. In this case,the diode is formed by the body diode of the enhancement MOSFET.Everything that has been explained concerning the implementation of theactive drift region with the second transistors 3 ₀-3 _(n) herein beforeapplies to the implementation of the active drift region 3 of FIG. 29accordingly.

A circuit arrangement as explained before with a first transistor 1 anda series circuit with second transistors 3 ₀-3 _(n) connected inparallel to the drift region of the first transistor or a circuitarrangement with a first transistor 6 and a series circuit with secondtransistors 3 ₀-3 _(n) connected in series with the load path of thefirst transistor 6 can be used like a conventional transistor, inparticular like a conventional MOSFET.

FIG. 30 illustrates one possible application of such circuitarrangement. Reference character 10 in FIG. 30 denotes one of thecircuit arrangements with a first transistor 1 or 6 respectively, and aseries circuit with second transistors 3 ₀-3 _(n) as explained before.This transistor 10 with the active drift region (ADR) or active driftzone (ADZ) will be referred to as ADR transistor 10 in the following.The ADR transistor 10 has a gate terminal G, formed by the gate terminalof the first transistor, a source terminal S formed by the sourceterminal of the first transistor and a drain terminal D₃ that is eitherformed by the drain terminal of the first transistor and/or by a drainterminal of the second transistor 3 _(n) arrangedmost distant to thefirst transistor in the series circuit with the second transistors 3 ₀-3_(n).

FIG. 30 illustrates the use of the ADR transistor 10 in a voltageconverter, in particular in a switched-mode voltage converter having aflyback-converter topology. This voltage converter includes inputterminals 201, 202 for applying an input voltage Vin and outputterminals 203, 204 for providing an output voltage Vout. The voltageconverter serves to convert the input voltage Vin into the outputvoltage Vout. The converter includes a transformer 210 with a primarywinding 211 and a secondary winding 212. The ADR transistor 10 isconnected in series with the primary winding 211, where the seriescircuit with the primary winding 211 and the ADZ transistor 10 isconnected between the input terminals 211, 212. A control circuit 230 isconnected to the gate terminal of the ADR transistor 10 and isconfigured to provide a pulse-width modulated (PWM) drive signal S230 tothe gate terminal G of the ADR transistor 10 that cyclically switchesthe ADR transistor 10 on and off, when the voltage converter is inoperation. When the ADR transistor 10 is cyclically switched on and off,a PWM square voltage is generated at the secondary winding 212 of thetransformer 210, where this PWM square voltage is rectified by arectifier arrangement 220 connected between the secondary winding 212and the output terminals 203, 204. The rectifier arrangement 220 may,for example, include at least one rectifier element, such as a diode,and a capacitor.

The output voltage Vout can be controlled by controlling the duty cycleof the PWM drive signal S230 provided by the control circuit 230. Forthis, the control circuit 230 may receive an output voltage signalS_(Vout) that is representative of the output voltage Vout. Generatingand transmitting this output voltage S_(Vout) to the control circuit 230is commonly known, so that no further explanations are required in thisregard. Further, the control circuit 230 may receive a current signalS_(I) that represents a load current through the ADR transistor 10.Generating such a current signal S_(I) is also known, so that no furtherexplanations are required in this regard. Based on the output voltagesignal S_(Vout) and the current signal S_(I), the control circuit 230generates the PWM drive signal S230. A PWM control circuit thatgenerates a PWM drive signal from an output voltage signal and a currentsignal is commonly known, so that no further explanations are requiredin this regard.

The control circuit 230 includes power supply terminals, wherein asupply capacitance 231 is connected between these power supplyterminals. To enable the control circuit 230 to generate the PWM drivesignal S230 a supply voltage is required between the power supplyterminals, which means that the power supply capacitor 231 has to becharged before the ADR transistor 10 can be switched on for the firsttime. In operation of the voltage converter, which is when the ADRtransistor 10 is cyclically switched on an off, the power supplycapacitor 231 can be charged by an auxiliary winding 213 of thetransformer 210, where this auxiliary winding 213 is inductively coupledto the primary winding 211 and the secondary winding 212 and isconnected to the power supply capacitor 231 via a rectifier element 232,such as a diode.

At the time start-up of the voltage-converter, which is when the inputvoltage Vin is applied between the input terminals 201, 202 for thefirst time, the ADR transistor 10 is switched off. The input voltage Vintherefore mainly drops between the drain terminal D₃ and the sourceterminal S of the ADR transistor 10. Referring to FIG. 26, the ADRtransistor 10 has an output terminal 10 ₁ that is connected to thesupply capacitor 231 via the rectifier element 232. This output terminal10 ₁ is connected to a tap of the series circuit of the secondtransistors and provides an output voltage that is lower than the inputvoltage Vin and that is suitable to charge the supply capacitor 231.

FIG. 31 illustrates an embodiment of the ADR transistor 10 in detail.For a better understanding, the rectifier elements 232 and the supplycapacitor 231 are also illustrated in FIG. 27. Referring to FIG. 31, theoutput terminal 10 ₁ is connected to a tap between two of the secondtransistors, wherein in the embodiment according to FIG. 30, the outputterminal 10 ₁ is connected to a tap between the second transistors 3 ₁and 3 ₂. When the ADR transistor 10 is in the off-state, it acts like avoltage divider, so that the voltage at the output terminal 10 ₁ islower than the overall voltage between the drain terminal D₃ and thesource terminal S. The desired output voltage at the output terminal 10₁ can be adjusted by suitably selecting the tap, where the outputvoltage is lower at taps arranged closer to the first transistor 6 thanat taps arranged more distant to the first transistor 6.

Referring to FIG. 31, optionally a resistor 233 is connected between theoutput terminal 10 ₁ and the supply capacitor 231. This resistor mayhelp to limit a charging current to the supply capacitor 231. Further, aswitch 234 can be connected between the output terminal 10 ₁ and thecapacitor 231. Through this switch 234 the charging mechanism thatcharges the supply capacitor 231 via the output terminal 10 ₁ can bedeactivated when the voltage converter is in operation, which is whenthe auxiliary winding 213 provides the charging current to the capacitor231.

FIGS. 32 and 33 illustrate two additional embodiments of chargingcircuits using the ADR transistor 10 for charging a capacitor 231, suchas a supply capacitor.

In the embodiment illustrated in FIG. 32, the rectifier element 232 isconnected to a first tap of the ADR transistor 10 and a voltage limitingelement 235, such as a Zener or Avalanche diode or a series circuit ofZener or Avalanche diodes, is connected to a second tap of the ADRtransistor 10. The first tap is arranged closer to the first transistor6 than the second tap in the series circuit of the second transistors 3₀-3 _(n). The voltage limiting element 235 is connected between thecapacitor 231 and the second tap. In this circuit the capacitor 231 isdischarged via the voltage limiting element whenever the voltage acrossthe capacitor 231 is higher than the electrical potential at the secondtap plus the limiting voltage of the voltage limiting element. Theoperating principle of the circuit according to FIG. 32 is as follows:When the ADR transistor is switched off so that the electricalpotentials at the individual taps increase, the capacitor is charged tothe electrical potential of the first tap minus the forward voltage ofthe diode 232. When the voltage across the series circuit with thesecond transistors 3 ₀-3 _(n) further increases so that the electricalpotential at the second tap becomes higher than at the first tap, thecapacitor is further charged, namely to the electrical potential at thesecond tap minus the forward voltage of the Zener diode 235. In eachcase, the capacitor 231 is only discharged when the first transistor 6is switched on and when the electrical potential at the second tapdecreases to the voltage V231 of the capacitor minus the breakthroughvoltage of the Zener diode 235. Thus, the voltage V231 of the capacitoris in accordance with a hysteresis curve.

In the embodiment illustrated in FIG. 33, a further rectifier element236, such as a diode is connected between the capacitor 231 and thesecond tap. In this circuit a voltage V231 having a hysteresis isgenerated across the capacitor when the ADR transistor is switched offand on. When the ADR transistor 10 is switched off and the electricalpotential at the first tap increases, the capacitor 231 is charged to anelectrical potential approximately corresponding to the electricalpotential at the tap (the forward voltage of the diode 232 is usuallynegligible relative to the voltage at the first tap). When the ADRtransistor is switched on so that the electrical potential at the secondtap decreases, the voltage V231 approximately corresponds to theelectrical potential at the second tap (the forward voltage of thefurther diode 236 is usually negligible relative to the voltage at thesecond tap), where the electrical potential at the second tapapproximately corresponds to source potential when the ADR transistor iscompletely switched on.

Instead of using the output terminal 10 ₁ for charging a supplycapacitor 231, the output terminal 10 ₁ could also be used for simplymeasuring the voltage drop within the ADR transistor 10.

Although various exemplary embodiments of the invention have beendisclosed, it will be apparent to those skilled in the art that variouschanges and modifications can be made which will achieve some of theadvantages of the invention without departing from the spirit and scopeof the invention. It will be obvious to those reasonably skilled in theart that other components performing the same functions may be suitablysubstituted. It should be mentioned that features explained withreference to a specific figure may be combined with features of otherfigures, even in those cases in which this has not explicitly beenmentioned. Further, the methods of the invention may be achieved ineither all software implementations, using the appropriate processorinstructions, or in hybrid implementations that utilize a combination ofhardware logic and software logic to achieve the same results. Suchmodifications to the inventive concept are intended to be covered by theappended claims.

What is claimed is:
 1. A semiconductor device arrangement, comprising: anormally-off device having a load path between load terminals; and aplurality of normally-on devices, each having a load path between afirst load terminal and a second load terminal and a control terminal;wherein the normally-on devices have their load paths connected inseries and connected in series to the load path of the normally-offdevice, and wherein each but one of the normally-on devices has itscontrol terminal connected to the load terminal of another one of thenormally-on devices.
 2. The semiconductor device arrangement of claim 1,wherein one of the normally-on devices has its control terminalconnected to one of the load terminals of the normally-off device. 3.The semiconductor device arrangement of claim 1, wherein one of thenormally-on devices has its load path directly connected to the loadpath of the normally-off device and has its control terminal connectedto a first load terminal of the normally-off device; and wherein each ofthe other normally-on devices has its control terminal connected to afirst load terminal of an adjacent normally-on device.
 4. Thesemiconductor device arrangement of claim 1, wherein the normally-offdevice and/or one or more of the normally-on devices is one of a MOSFET,a MISFET, a MESFET, an IGBT, a JFET, a HEMT, a FINFET, a nanotubedevice.
 5. The semiconductor device arrangement of claim 1, wherein thenormally-off device and/or the normally-on devices comprise one of thefollowing materials or compositions thereof: Si, SiO, SiN, Ge, Ga, Al,GaAs, GaN, carbon, In, InP, SiC.
 6. The semiconductor device arrangementof claim 1, wherein the normally-on devices are normally-on transistors.7. The semiconductor device arrangement of claim 1, wherein thenormally-on devices are one of n-channel or p-channel transistors. 8.The semiconductor device arrangement of claim 1, wherein the normally-ondevices are implemented as FINFETs, each comprising: at least onesemiconductor fin; a source region, a body region and a drain regionarranged in the at least one semiconductor fin, with the body regionbeing arranged between the source region and the drain region; and agate electrode arranged adjacent to the body region and dielectricallyinsulated from the body region by a gate dielectric.
 9. Thesemiconductor device arrangement of claim 8, wherein the source anddrain regions are arranged distant in a longitudinal direction of thesemiconductor fin.
 10. The semiconductor device arrangement of claim 9,wherein the at least one semiconductor fin includes sidewalls andwherein the gate electrode is arranged at least on one of the sidewallsof the semiconductor fin.
 11. The semiconductor device arrangement ofclaim 9, wherein one FINFET further comprises: a source electrodeconnected to the source region; and a semiconductor region dopedcomplementarily to the source region and connected to the sourceelectrode.
 12. The semiconductor device arrangement of claim 9, whereinthe normally-off device is implemented as a FINFET comprising: at leastone semiconductor fin; a source region, a body region and a drain regionarranged in the at least one semiconductor fin, with the body regionbeing arranged between the source region and the drain region; and agate electrode arranged adjacent to the body region and dielectricallyinsulated from the body region by a gate dielectric.
 13. A semiconductordevice arrangement, comprising: a normally-off device having a load pathbetween load terminals; and a plurality of normally-on devices, eachhaving a load path between a first load terminal and a second loadterminal and a control terminal; wherein the normally-on devices havetheir load paths connected in series and connected in series to the loadpath of the normally-off device, and wherein one of the normally-ondevices has its control terminal connected to one of the load terminalsof the normally-off device.
 14. The semiconductor device arrangement ofclaim 13, wherein each but the one of the normally-on devices has itscontrol terminal connected to the load terminal of another one of thenormally-on devices.
 15. A circuit arrangement comprising: a devicearrangement with a normally-off device having a load path and with aplurality of normally-on devices, each having a load path between afirst and a second load terminal and a control terminal, wherein thenormally-on devices have their load paths connected in series andconnected in series to the load path of the normally-off device, andwherein each but one of the normally-on devices has its control terminalconnected to the load terminal of another one of the normally-ondevices, and wherein one of the normally-on devices has its controlterminal connected to one of the load terminals of the normally-offdevice; and a capacitive storage element connected to the load terminalof one of the normally-on devices.
 16. The circuit arrangement of claim15, further comprising: a control circuit, wherein the capacitivestorage element is connected to supply terminals of the control circuit.17. The circuit arrangement of one of claim 16, wherein the controlcircuit is configured to provide a pulse-width modulated signal to thenormally-off device.
 18. The circuit arrangement of claim 15, furthercomprising: a load connected in series with the device arrangement, aseries circuit with the device arrangement and the load being connectedbetween input terminals that are configured to have an input voltageapplied thereto.
 19. The circuit arrangement of claim 18, wherein theload comprises: a transformer with a first winding connected in serieswith the device arrangement and with a second winding inductivelycoupled with the first winding; and a rectifier arrangement coupled tothe second winding and comprising out-put terminals configured toprovide an output voltage.